Various oncogenic viruses appear to malignantly transform a cell by raising the level of a normal cellular protein. In addition, different viruses can act by increasing different proteins; and elevated levels of a given protein may transform only specific cell types. This apparent complexity only points out how little we know about the controls that stablilize the differentiated state, one could then use this information to determine how transformation manipulates these control elements. Our approach, therefore, is to first elucidate the molecular mechanisms by which cultured avian tendon cells maintain the in vivo level of their principle differentiated product, collagen. An aid to this problem is the ability of ascorbate in cultured tendon cells to specifically modulate the level of collagen synthesis--mimicking ascorbates role in curing scurvy. Understanding how a small molecule can interact with the cell to alter the relative levels of tissue-specific protein synthesis will resolve those steps in the collagen biosynthetic pathway that are rate limiting. With knowledge of how the normal cell stabilizes the differentiated state, we will be able to analyze how malignant transformation manipulates these control steps. Specifically, we want to determine the mechanism that causes a sharp decline in yhe level of collagen synthesis after infection with Rous sarcoma virus, hat contrasts directly with the increase observed for most proteins. Using a temperature senstivie mutant in the "src" gene, we will be able to kinetically observe at what stage transformation distrupts the flow of intermediates through the collagen biosynthetic pathway. By understanding in detail how one type of malignant transformation interferes with the regulation of a differentiated function, we will be in a better position to generalize about what characterizes the oncogenic state. Finally, we will develop optimum cell culture conditions - for proliferation and expression of differentiated function - for mouse tendon cells as already accomplished for the chick cells. This will enable use to compare the regulation of collagen synthesis in mammalian to that in avian cells. Moreover, various mouse mutants with connective tissue disorders can then be studied in culture in a permissive environment for collagen expression.